Adding default values programmatically

I have a number of matrix components and I need to add default values programmatically. The data sources are a few Excel files.

Here is my plan. Would you please give me some advice?

1. Create a matrix component (i.e.: a 2x2 matrix)
2. Create a custom module admin interface, upload an Excel file
3. Write a custom module to extract data from an Excel file, and populate the matrix. Only use the leftmost 2x2 table of the Excel file, ignore all other cells.
4. Site admin would need to replace an existing Excel file shall default values of the matrix need to change

Are there specific APIs to populate the matrix component? Or shall I use field api?

Thank you.